A body frame structure of a railway vehicle that includes vertically and horizontally arranged first and second frame members weld-joined to an outer panel with an end portion of the second frame member facing a side surface of the first frame member is already known (see, for example, Patent Document 1). As shown in FIGS. 7A and 7B, in the configuration of such a body frame structure, a side surface of a vertical frame member a having a hat-shaped cross-section faces an end portion of a horizontal frame member b having a hat-shaped cross-section. In the facing area, flanges b1 of the horizontal frame member b are placed on a flange a1 of the vertical frame member a in an overlapping manner. The frame members a and b including the overlapping area are spot-welded to an outer panel c at welding points d in the manner shown in FIG. 7C.
However, in the above joint structure, the vertical frame member a and the horizontal frame member b are simply joined with the flanges a1 and b1 overlapping with each other, and the material and structural characteristics of the hat-shaped cross-section are not effectively utilized. Therefore, even with such a hat-shaped cross-section the joint strength of this joint structure is low, and the buckling strength of the outer panel cannot be improved. In view of the above, in the body frame structure described in Patent Document 1, a joint plate e shown by phantom lines in FIGS. 7A and 7B is placed on the frame members a and b and is spot-welded at weld-joining points d to obtain the required strength.
[Patent Document 1] Japanese Patent Application Laid-Open No. H09-30414.